Field of the Invention
This invention relates to a method of heat treating a zone of each of a plurality of articles.
It is well known to heat treat the tips of fasteners, particularly but not exclusively, so called "self threading" fasteners, to harden the tips thereof to improve the performance of the fasteners in cutting a thread in a substrate.
GB-A-1376026 discloses an apparatus in which an induction heater is utilised to perform heat treatment there being a raceway to feed the fasteners in succession, in abutting relationship, towards the induction heater. The fasteners are pushed one at a time from the raceway such that the rate at which the fasteners are fed towards the heater depends entirely upon the rate of operation of the pusher.
The dwell time of the fasteners in the heater is controlled by the rate of operation of the pusher and a feed off mechanism which together cause the fasteners to be removed one at a time from the heater and passed to a further raceway where they pass through a quenching station. The rate at which the articles pass through the quenching station is controlled by a regulator.